The present invention relates to a plasmid containing simian immunodeficiency virus (hereinafter referred to as xe2x80x9cSIVxe2x80x9d)-derived genes.
Particularly, the present invention relates to the plasmid pSIV/GE which contains gag, protease, env and rev gene, all derived from SIV, but not tat and nef gene and the plasmid pSIV/pol which contains SIV-derived pol gene; the plasmid pHIV/GE and pHIV/pol that are substituted the SIV-derived genes in the plasmid pSIV/GE and pSIV/pol by human immunodeficiency virus (hereinafter referred to as xe2x80x9cHIVxe2x80x9d)-derived corresponding genes; AIDS DNA vaccine containing the plasmid pSIV/GE and pSIV/pol; and AIDS DNA vaccine containing the plasmid pHIV/GE and pHIV/pol.
It has been found that plasmid DNA, when injected into mice without being associated with any adjuvant, can generate antibody and CTL responses to viral antigens encoded by the plasmid DNA, and elicit protective immunity against viral infection (Ulmer at al., Science, 259:1745, 1993). Starting from this, there have been reported many research results regarding the induction of humoral and cellular immune responses resulting from the introduction of DNA vaccines containing various viral genes in animal models (Chow et al., J. Virol., 71:169, 1997; McClements et al., Proc. Natl. Acad. Sci. USA, 93:11414, 1996; Xiang et al., Virology, 199:132, 1994; Wang et al., Virology, 211:102, 1995; Lee et al., Vaccine, 17:473, 1999; Lee et al., J. Virol., 72:8430, 1998).
DNA vaccines are highly safe, as proven by the fact that the clinical testing of DNA vaccines on human beings was allowed by the FDA of U.S.A. only four years after great success was reported in the research using small animals. With the advantage of being able to induce potent and persistent cellular immune responses, DNA vaccines have been considered strong candidates for prevention and therapy of AIDS.
In connection to candidates for AIDS vaccines, attenuated viruses, subunit vaccines, and live virus vector vaccines have been under study. Of these candidates, attenuated viruses induce the most potent immune responses, but have the danger of being converted into virulent strains since they can replicate in the host. In fact, the infection of some attenuated viruses caused AIDS in experiments on monkeys, raising concerns about their safety.
On the other hand, subunit vaccines suffer from the problem of being unable to induce CTL immune responses necessary for protection against HIV. In the case of live virus vector vaccines, questions have been raised whether the vectors themselves may cause infection and diseases.
For vaccines against HIV to be applied to humans, their virtues must be first confirmed through testing on primates. Primate animal models for use in infection and vaccination ranging from HIV/chimpanzee model to SIVmac/rhesus monkey model, are discriminately employed in consideration of the severity of the diseases caused and the difficulty in inducing protective immune responses in them.
Particularly, rhesus monkey models are quite difficult to protect from infection by SIVmac virus and SIVmac/rhesus monkey models, that is, rhesus monkey models infected by SIVmac virus, are recognized as being the closest model to HIV-infected humans (Hanke et al., J. Virol., 73:7524, 1999). SIVmac/rhesus monkey models are very similar to HIV-1 infected humans in the following aspects:
1) host immune response after infection,
2) route of infection,
3) occurrence of persistent infection,
4) disease induction in association with a decrease in CD4+ cell number,
5) impossibility of preventing the infection by use of neutralizing antibodies alone, and
6) pattern of viral loads in infected host.
With these close similarities, SIVmac/rhesus monkey models, in spite of SIVmac being different from HIV in base sequence, are recognized as the most preferable animal models. AIDS DNA vaccines developed so far are reported to inhibit AIDS infection in the animal models which are most easily protected like HIV/chimpanzee models. However, chimpanzees are not the best models since AIDS does not occur in HIV-infected chimpanzees.
Another animal model, chimeric simian-human immunodeficiency virus (SHIV)/monkey model, was designed for evaluating the efficacy of envelope-based HIV-1 vaccines. At the time when SHIV was first created, it did not induce disease in monkeys, but after having undergone repeated in vivo passage, some SHIV was transformed into virulent mutants which are able to cause a fatal disease in monkeys (Reimann et al., J. Virol., 70:6922, 1996). However, SHIV has the drawback of being an artificial recombinant virus which does not exist in the natural environment.
Accordingly, the SIVmac/rhesus monkey model is considered to be the most preferable in evaluating the efficacy of AIDS vaccines. According to what is known thus far, the SIVmac/rhesus monkey model was successfully protected from SIV infection only when attenuated viruses, whose safety in humans is in question, were used (Daniel et al., Science, 258:1938, 1992), but failed to be protected from SIV when using other types of vaccines, including DNA vaccines (Lu et al., J. Virol., 70:3978, 1996). Thus, there remains an urgent need to develop a DNA vaccine capable of directing protection against SIV infection in SIVmac/rhesus monkey models.
Among plasmid DNA vaccines which have failed to induce protection in SIVmac/rhesus monkey models, thus far, there are plasmids which not only carry gag, env, and rev genes together, but also code for accessory proteins such as tat, nef, vpr, and vpx, and plasmids which anchor env genes sourced from various species (Lu, et al., J. Virol., 70:3978, 1996).
In a study using a plasmid carrying an env gene of HIV and a plasmid carrying a gag/pol gene, an HIVSF/chimpanzee model succeeded the protection (Boyer et al., Nat. Med., 3:526, 1997). However, since HIV/chimpanzee model is easy to generate the protective responses by immunization, it is likely that these plasmids will not show similar immune effects, raising the question whether they can effectively function as AIDS vaccines in humans.
The AIDS vaccines used in the prior study is believed to fail to induce effective protection against SIVmac infection for the following reasons. First, based on the research report that accessory genes of HIV, such as nef and tat, inhibit and disturb immune responses in vitro (Lindemann et al., J. Exp. Med., 179:797, 1994; Viscidi et al., Science, 246:1616, 1989), those genes, if used as immunogens, may negatively affect the induction of protective immune responses against AIDS virus in humans and monkeys. Next, effective use was not made of a pol gene, a HIV gene encoding many CTL markers (epitopes), which are known to play an important role in protective immune responses.
Thus far, the successful immune protection generated in SIVmac/rhesus monkey models was unique among attenuated viruses, whose safety in humans is in question (Daniel et al., Science, 258:1938, 1992). Accordingly, if any plasmid DNA vaccine successfully induces protection in SIVmac/rhesus monkey models, the plasmid DNA itself can be evaluated as an effective AIDS vaccine and thus be applied to humans.
Leading to the present invention, the intensive and thorough research on excellent protection against AIDS virus, conducted by the present inventors aiming to circumvent above problems encountered in prior arts, resulted in the finding that a plasmid carrying a combination of gag, protease, env and rev genes or a combination of genes coding for reverse transcriptase and integrase, respectively, can induce excellent protective effects in SIVmac/rhesus monkey models with great safety.
It is an object of the present invention to provide a plasmid vaccine capable of inducing protective effects in SIVmac/rhesus monkey models.
It is another object of the present invention to establish a plasmid immunogen which can be used in the prophylaxis and therapy of human AIDS caused by HIV.
In accordance with the present invention, the foregoing objects and advantages are readily obtained.
The present invention provides a plasmid carrying gag, protease, env and rev genes, all derived from SIV, but not tat and nef genes and a plasmid carrying a SIV-derived pol gene encoding for a reverse transcriptase and an integrase.
The present invention also provides plasmids in which the SIV genes are substituted by corresponding HIV-derived genes.
In addition, the present invention provides DNA vaccines comprising combinations of the plasmids carrying SIV-derived genes or the plasmids carrying HIV-derived genes.
Further features of the present invention will appear hereinafter.